1. Field of the Invention
The present invention relates to a poly(ester-amide) hot melt adhesive composition, to a method of filling voids with the adhesive composition and to articles filled or coated with the hot melt adhesive composition. More particularly, it refers to a block copoly(ester-amide) filled with a finely divided metal powder, to a method of filling voids with such a composition and to articles, filled or coated with the composition.
2. Description of the Prior Art
Hot melt adhesives are well known in the prior art. These materials are conveniently applied to a substrate in the molten state and upon cooling form an adhesive bond. However, a deficiency common to most of the hot melt adhesives of the prior art is their tendency to soften and flow at elevated temperatures, as, for example, 70.degree. to 100.degree. C. with a resulting loss of bond strength. Consequently, these materials are not suitable for use over a broad temperature range.
Attempts to upgrade the softening and flow temperatures have involved using a very high molecular weight resinous materials and/or crosslinking of the resin. These methods have resulted in materials with higher softening points and flow temperatures. However, in most cases the resulting material was not adapted to thermal processing because of its higher molecular weight and/or crosslinked structure resulting in extremely high application viscosity. Thus, these materials were not suitable for use as hot melt adhesives.
A definite need exists in the art for a hot melt adhesive which is resistant to flow at temperatures around 150.degree. C. but which can be readily processed and applied using hot melt adhesive application techniques and apparatus.
U.S. Pat. No. 3,650,999 discloses a poly(ester-amide) resin having improved adhesion and high temperature performance obtained by reacting a crystalline polyester, a C.sub.18 to C.sub.54 polycarboxylic acid and a primary diamine. However, this poly(ester-amide) in common with other hot melt adhesives has deficiencies in creep resistance at temperatures above 150.degree. C. in the range up to 205.degree. C. and above and in shrinkage when the hot melt is cooled to room temperature after application.
A definite need therefore exists in the art for a hot melt adhesive which has improved creep resistance and shrink resistance without loss in processability and ease of application.
In the manufacture and repair of metal bodies such as automobiles and appliances, solder compositions containing lead are frequently used to fill cavities and voids. These lead solders are a health hazard which mandates special handling to protect workers and are also extremely dense. Conventional hot melt adhesives are not satisfactory for such cavity and void filling applications because they cannot be sanded rapidly at assembly line speed, they do not readily accept paint because they bleed through, and they do not withstand the curing temperatures for the paint. Curable adhesives such as epoxies are generally unsatisfactory because they require careful metering of the components to provide good physical properties and bond strength, and because they take too long to cure to a sandable state.
A need therefore exists for a cavity or void forming composition which is less dense and toxic than lead solder, forms a strong bond to metal substrate, withstands extremes of humidity and temperature, is readily applied and rapidly sets to a sandable state, is easily sanded smooth, and accepts paint without bleeding through.